利用DCT系数计算两幅图像之间的相似度

Visual image retrieval on compressed domain with Q-distance

Hong Heather Yu

Panasonic Information and Networking Technology Lab.

heathery@

Abstract

This paper proposes a new image retrieval scheme that works directly on compressed image(JPEG)databases.As we know,a large percentage of the image databases are stored in compressed image format,such as JPEG format.In addition,about half of the images on the Internet are also in JPEG format.Thus,image retrieval systems that require JPEG decompression greatly limit the speed of image searching.Subsequently,new methodologies for retrieving of images without JPEG decoding is needed for web image search and compressed image database retrieval.In this paper,we propose a new metric,Q-distance, that can be utilized to measure the distance between two compressed images.A system that uses Q-distance for fast image retrieval is also presented.Experiment results show that Q-distance is robust against variation and this new retrieval scheme,which directly works on compressed image domain,is fast to execute and suitable for web image searching and retrieval.

1.Introduction

1.1Motivation

A study by Euro-marketing shows that there are over157million people worldwide who have access to the Internet,the gigantic multimedia information database.Needless to say,one of the most important functions of the Internet is'search'.The overwhelmingly available multimedia on such high traffic Internet demand fast searching and browsing capability of text,audio,as well as visual data.Since most of the images on the Internet are in compressed formats,it is therefore important to develop techniques that can allow visual image searching without image decompression,that is,directly search on compressed image domain.

As we know,a compressed image,such as JPEG image,can compress an image whereas keeping the visual quality of it by discarding the small high frequency coefficients.This means by throwing away the least significant coefficients,the visual appearance of an image does not change significantly,i.e.,the overall structure of an image is kept in the significant coefficients.Is this characteristic useful in designing similarity-based image retrieval systems?Can this property be employed to design a compressed-domain image search engine?In this paper,we present such an image search engine and show that this characteristic of visual media is indeed helpful in designing a compressed-domain image retrieval ware.Why?With regards to image retrieval,many real world scenarios emphasize on the similarity of the overall structure of images.For instance,on web image searching,users may have a rough idea of the image they are looking for.Hopefully,a simple sketch of the overall structure of the image can help them to find the image in the database.This requires a good distance measurement between the query sketch and the images in the database.In this paper,we